gwicke wrote:My understanding is that the only substantive camber changes with a 4:2:1
I'm not sure I understand what do you mean "substantive camber change", but there is just different pulling ratios (between the mixers) and different line row locations. 4:2:1 mixer is a linear one, so if line rows are located similarly (evenly from A), there will be no camber change when AoA changes. But if line row locations are chosen uneven manner it is possible to control camber when AoA changes.
Keeping line rows close to even spaces from each other is more reasonable than having them unevenly. Both for less drag and some structural reasons. Here 4:2:1 is better, and it is simpler too.
gwicke wrote:Slower AOA change along A-B is a good point, especially in very overpowered conditions with C and Z slack.
When overpowered and sheeted out foil kite flies very much on A lines only. Then only chosen airfoil defines how much camber there is. Usually it is quite low ("flat profile"), otherwise depower and stability are not available. I have test flied some of my kites with A line bridles only, it is the ultimate test for kite stability and depower.
Usually line rows are located a bit further from A than mixer pulling ratio would suggest. Then there is some more camber when sheeted in, which is useful (more power, later backstall). Exception is brakes, which can be at 95%, so they are pulled more than "should", again having more effect/camber (last 5% of the kite will follow).
Diablo line does this even more when it engages at the final part of the sheeting in. If kite tolerates it (no backstall) no doubt it is useful, especially at downwind legs.
If line rows are located evenly (for 4:2:1) then it is decided just AoA change is enough to power the kite. If lines B-C were located closer to A than pulling ratio demands, kite would decrease its camber at higher AoA - not a very good idea.